Air-bag device

ABSTRACT

In an airbag ( 2 ), a length extending from a sewn portion ( 10 ) to a right periphery of a presser plate ( 13 ) is set such that a length (L 1 ) is shorter than a length (L 2 ) wherein the length (L 2 ) is at an attachment side base cloth ( 3 ) side and the length (L 1 ) is at a cloth-like piece ( 9 ) side. When the airbag ( 2 ) is expanded in emergency situations, the attachment side base cloth ( 3 ) is expanded while it moves away outwardly from the cloth-like piece ( 9 ), thereby opening a vent hole ( 8 ), so that the airbag ( 2 ) is eased in abrupt expansion directing toward an occupant. When the airbag ( 2 ) becomes a sufficient size to protect the occupant, it bends instantaneously a retaining plate ( 17 ) to release the parallel portion ( 9 B) of the cloth-like piece ( 9 ) from the presser plate ( 13 ), so that the cloth-like piece ( 9 ) is brought into intimate contact with the attachment side base cloth ( 3 ) to close the vent hole ( 8 ), thereby protecting the occupant with reliability.

FIELD OF THE INVENTION

The invention relates to an airbag device whose airbag is deployable atthe time of collision of a vehicle to protect an occupant, moreparticularly to an airbag device capable of precisely controlling anexpansion speed of an airbag in the midway of the expansion.

BACKGROUND OF THE INVENTION

An airbag device fitted to a driver seat and a passenger seat of avehicle is to protect an occupant by rapidly expanding an airbag bymeans of a gas pressure let out from an inflator at the time ofcollision of the vehicle. In the airbag device described above, it isnecessary to ease influence of impact given to the occupant when theairbag is expanded, thereby receiving the occupant softly by the airbag.To that end, it is preferable to avoid a situation where the airbag isabruptly expanded to protrude toward the occupant when the inflatoroperates. Particularly, since the occupant comes into contact with theairbag in a short time in the case where the occupant sits down adjacentto the airbag device, it is preferable to avoid a situation where theairbag is abruptly expanded to protrude toward the occupant.

For a device for controlling the expansion speed of the airbag describedabove, various technologies for adjusting opening and closing degree ofa vent hole of the airbag are developed. For example, JP 11-334521A(patent reference 1) proposes a device for opening and closing the venthole by an actuator. In this example, there are provided an actuatormade of a plate-like piezoelectric element and a vent hole openable andclosable by the actuator, respectively, formed on a retainer forsupporting an inflator and an airbag, wherein an internal pressure atthe beginning of the expansion of the airbag is detected by a pressuresensor, and it is decided that the occupant approaches the airbag whenthe internal pressure is higher than a pressure at normal time, therebyenergizing the actuator to operate it, so that the vent hole is openedthrough which gas inside the airbag is discharged outward.

Further, JP 11-105664A (patent reference 2) proposes a device forclosing a vent hole by a valve for regulating volume of gas to be letout which is formed of the same base cloth as an airbag. In thisexample, when the valve for regulating volume of gas to be discharged istemporarily stopped by a tacking thread and the like, a state where thevent hole keeps open is maintained, thereby controlling an expansionspeed at the beginning of the expansion of the airbag. Thereafter, whenthe airbag is expanded, and a stretching force of the airbag becomeslarger than a tacking force of the tacking thread, the tacking thread iscut so that the vent hole is throttled by the valve for regulatingvolume of gas to be discharged. As a result, the gas inside the airbagis restrained from being discharged outward so that the airbag isexpanded until it becomes a suitable size to protect the occupant.

However, since the device in the patent reference 1 has a structure toclose the vent hole by operating the actuator made of the plate-likepiezoelectric element and the like, there is a drawback in that amechanism to close the vent hole is complex and expensive, and also aresponse speed is slow. Further, since the patent reference 2 has asystem to close the vent hole by cutting the tacking thread by thestretching force of the airbag, there is a drawback in that timing forclosing the vent hole is varied largely due to the variations of abreaking force of the tacking thread and the stretching force of theairbag, and also the timing for closing the vent hole can not be changedin response to a driving posture of the occupant.

SUMMARY OF THE INVENTION

The invention has been made in view of the technical problems of theprior arts described above and it is a first object of the invention toprovide an airbag device having a closing mechanism of a vent hole whichis simple and manufactured at low cost and the closing of the vent holecan be effected with reliability.

It is a second object of the invention to provide an airbag devicecapable of discharging gas from the vent hole with reliability.

It is a third object of the invention to provide an airbag devicecapable of protecting an occupant with reliability by closing the venthole in a short time.

It is a fourth object of the invention to provide an airbag devicecapable of closing the vent hole and switching of the developing heightof an airbag with good timing.

(1) An airbag device in the first aspect of the invention comprising aninflator for generating gas and an airbag expandable by the gas, saidairbag device is provided with a gas inflow port provided in the airbagthrough which the gas flows in, a vent hole provided in the airbag fordischarging the gas flown in the airbag, a cloth-like piece connected toa vicinity of the vent hole at one end thereof, and to a vicinity of thegas inflow port at the other end thereof releasably, wherein saidcloth-like piece does not close the vent hole in a state where the otherend is retained, and closes the vent hole due to an internal pressure ofthe airbag in a state where the other end is released, a retainingdevice for retaining the other end of the cloth-like piece, andreleasing means for releasing retention of the retaining device.

(2) The airbag device described under item (1) as above, wherein alength of the cloth-like piece from one end to the other end is shorterthan a length of the airbag from one end to the other end.

(3) The airbag device described under item (1) or (2) as above, whereinthe cloth-like piece is connected to an inside of the airbag at one endat the position in the vicinity of the vent hole and remote from the gasinflow port.

(4) An airbag device comprising an inflator for generating gas and anairbag expandable by the gas, said airbag device is provided with a gasinflow port provided in the airbag through which the gas flows in, avent hole provided in the airbag for discharging the gas flown in theairbag, a cloth-like piece connected to an inside of the airbag at bothends thereof and spaced apart from an edge of the vent hole, anextension cloth connected to the cloth-like piece at one end, to thevicinity of the gas inflow port at the other end to be releasable,wherein said extension cloth does not close the vent hole in a statewhere the other end is retained, and closes the vent hole due to aninternal pressure of the airbag in a state where the other end isreleased, a retaining device for retaining the other end of thecloth-like piece, and releasing means for releasing retention of theretaining device.

(5) The airbag device described under any one of items (1) to (4),wherein the retaining device has a retaining plate, and the releasingmeans implements releasing by forcibly deforming the retaining plate.

(6) The airbag device described under item (5) as above, wherein thereleasing means implement releasing by forcibly deforming the retainingplate by a pressure generated by an explosive.

(7) The airbag device described under any one of items (1) to (6) asabove, wherein the airbag is provided with a tether belt for restrainingexpansion of the airbag, and one end of the tether belt is retained bythe retaining device.

According to the invention as set forth in the above items (1), (2), (3)and (4), the vent hole can be closed by merely releasing retention ofthe other end of the cloth-like piece, so that a closing mechanism ofthe vent hole is simple and low in cost and the closing of the vent holecan be carried out with reliability. Further, since gas can bedischarged through the vent hole by way of a pocket functioning as a gasreservoir, impact to be applied to the occupant at the time of expansionof the airbag can be eased with reliability.

According to the invention as set forth in the above item (5), since thevent hole can be closed in a short time by releasing retention of thecloth-like piece by forcibly deforming the retaining plate, the occupantcan be protected with reliability.

According to the invention as set forth in the above item (6), since theretention of the cloth-like piece is released by forcibly deforming theretaining plate owing to explosion by the explosive, an actuator forreleasing retention is simple and the vent hole can be closed in a shorttime.

According to the invention as set forth in the above item (7), since thetether belt and the cloth-like piece are releasably retained by a commonretaining device, a structure of the retaining device is simple, and theclosing of the vent hole and the switching of the developing height ofthe airbag can be carried out with good timing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an airbag device according to a firstembodiment of the invention:

FIG. 2 is a sectional view taken along line A-A in FIG. 1 showing astate where a vent hole is opened;

FIG. 3 is a sectional view taken along line A-A in FIG. 1 showing astate where the vent hole is closed;

FIG. 4 is an enlarged sectional view taken along line B-B in FIG. 1;

FIG. 5 is a view as viewed from an arrow Z in FIG. 4;

FIG. 6 is a sectional view taken along line C-C in FIG. 5;

FIG. 7 is a plan view of an airbag device according to a secondembodiment of the invention;

FIG. 8 is a sectional view taken along line D-D in FIG. 7 showing astate where a vent hole is opened;

FIG. 9 is a sectional view taken along line D-D in FIG. 7 showing astate where the vent hole is closed;

FIG. 10 is an enlarged sectional view taken along line E-E in FIG. 7;

FIG. 11 is a view as viewed from an arrow Y in FIG. 10;

FIG. 12 is a sectional view taken along line F-F in FIG. 11;

FIG. 13 is a perspective view of a cloth-like piece of an airbag deviceaccording to a third embodiment of the invention;

FIG. 14 is a sectional view of FIG. 13 showing a state where a vent holeis opened; and

FIG. 15 is a sectional view of FIG. 13 showing a state where the venthole is closed.

BEST MODE FOR CARRYING OUT THE INVENTION

An airbag device according to the first embodiment of the invention isdescribed hereinafter with reference to the accompanying drawings. FIG.1 is a plan view showing a state where an airbag device 1 is expanded,which shows a state where an inflator is removed. FIG. 2 is a sectionalview taken along line A-A in FIG. 1 showing a state where the inflatoris fitted. As shown in FIG. 1 and FIG. 2, the airbag device 1 is formedof the airbag 2 comprised of an attachment side base cloth 3 having acircular shape and an opposed side base cloth 4 having also the circularshape wherein peripheries of the attachment side base cloth 3 andopposed side base cloth 4 are sewn together and reversed to form theairbag 2 having a bag-like shape. The attachment side base cloth 3 islocated at a side to be fitted to a vehicle together with the inflator 6while the opposed side base cloth 4 is located at a side to face theoccupant and receives the occupant when the airbag 2 is expanded. Theinflator 6 is fitted to a circular gas inflow port 5 formed on thecenter of the attachment side base cloth 3, and gas generated in theinflator 6 flows in the airbag 2 through the gas inflow port 5, toexpand the airbag 2 while developing the airbag 2 in a folded state.There are provided four bolt insertion holes 11A, 11B, 11C and 11D inthe attachment side base cloth 3 each spaced at 90 degrees at theperipheral portion of the gas inflow port 5 of the attachment side basecloth 3, and the airbag 2 is fitted to the vehicle using these boltinsertion holes 11A-11D.

FIG. 4-FIG. 5 show a detailed structure of a metal fitting portion bymeans of which the airbag 2 is fitted to the vehicle, wherein FIG. 4 isan enlarged sectional view taken along line B-B in FIG. 1 and FIG. 5 isa view as viewed from an arrow Z in FIG. 4. As shown in FIG. 4-FIG. 5,the attachment side base cloth 3 is clamped between a substantiallydisc-like presser plate 13 and a metal fitting 12, and it is fixed tothe metal fitting 12 together with a flange 6A of the inflator 6 by mansof four bolts 14A-14D inserted into four bolt insertion holes 11A-11Dand nuts 15 screwed into the bolts 14A-14D respectively. In the mannerdescribed above, the folded airbag 2 and the metal fitting 12 to whichthe inflator 6 is fitted are fixed to a central portion of a steeringwheel of the vehicle (not shown).

As shown in FIG. 1, three vent holes 7A, 7B and 8 are provided in theattachment side base cloth 3 for discharging gas flown in the airbag 2outward. Two vent holes 7A, 7B are formed at positions which are equallyspaced from a center 5A of the gas inflow port 5 in a radial direction,while the gas vent hole 8 is formed at a position spaced outwardly fromthe center 5A of the gas inflow port 5 in a radial direction, wherein adistance from the vent hole 8 to the center 5A is longer than that fromthe vent holes 7A, 7B to the center 5A. As shown by dotted lines in FIG.1, a cloth-like piece 9 for closing the vent hole 8 is fitted to theinside of the attachment side base cloth 3. The cloth-like piece 9 has alength extending outwardly from the peripheral portion of the gas inflowport 5 and exceeding the outer end of the vent hole 8, and it iscomprised of a parallel portion 9B extending outwardly in the radialdirection from the peripheral portion of the gas inflow port 5 and asemicircular portion 9A having a radius curvature which is larger thanthat of the vent hole 8, and made of a cloth which is the same materialas the airbag 2. The cloth-like piece 9 may be made of a cloth which isdifferent from the material of the airbag 2. Further, the cloth-likepiece 9 is not limited to a cloth and may be formed of a sheet-likematerial such as plastics and the like if the material has a flexibilitycapable of closing the vent hole 8. The cloth-like piece 9 is sewn andfixed to the attachment side base cloth 3 at coordinate axis position X2which is spaced by a distance d in an outward radial direction from acoordinate axis position X1 extending in the direction of X from thecenter 5A of the gas inflow port 5 to the edge of the vent hole 8 in theradial direction. A sewn portion 10 of the cloth-like piece 9 has acircular-arc shape and spaced from the edge of the vent hole 8. A widthW of the parallel portion 9B of the cloth-like piece 9 is set to belarger than a diameter of the vent hole and has a width which issufficient to completely close the vent hole 8. It is also possible tocontrol the vent hole 8 so as to discharge gas slightly, by making thewidth W of the parallel portion 9B of the cloth-like piece 9 smallerthan the diameter of the vent hole 8, without the vent hole 8 completelyclosed.

The parallel portion 9B is detachably fitted to a presser plate 13 atthe peripheral portion side of the gas inflow port 5. That is, as shownin FIG. 1, there are provided two retaining holes 16A, 16B in theattachment side base cloth 3 between the bolt insertion holes 11D, 11Calong the same circumference of the bolt insertion holes 11D, 11C. Anignitor insertion hole 23 through which an ignitor 20, described later,is inserted, is defined in the attachment side base cloth 3 between tworetaining holes 16A, 16B while a U-shaped notch 24 is formed on theparallel portion 9B so as to surround the ignitor insertion hole 23. Asshown in FIG. 4-FIG. 5, the parallel portion 9B is inserted in a gapbetween the presser plate 13 and the attachment side base cloth 3 whilethe two retaining holes 16A, 16B are positioned so as to align with twoholes 21A, 21B defined in the presser plate 13. Then a retaining plate17 is fixed to the presser plate 13 by way of bolts 14C, 14D, whileretaining projections 18A, 18B of the retaining plate 17 are insertedinto the retaining holes 16A, 16B through two holes 21A, 21B, therebyrestraining the parallel portion 9B from not being come off the presserplate 13.

An explosive chamber 19 protruding cylindrically toward the inside ofthe airbag 2 is formed on the retaining plate 17 at the intermediateportion between the retaining projections 18A and 18B, while theexplosive 19A is sealed in the explosive chamber 19. The ignitor 20 forigniting the explosive 19A is fitted to the flange 6A of the inflator 6,and the tip end of the ignitor 20 extends to a portion in the vicinityof the explosive 19A. Since necking portions 17A, 17A are provided onthe retaining plate 17, when the explosive 19A in the explosive chamber19 is exploded, the retaining plate 17 is bent along the neckingportions 17A due to gas pressure caused by explosion, as shown by twodotted chain lines in FIG. 6, to be subjected to plastic deformation, sothat the retaining projections 18A, 18B come off the retaining holes16A, 16B of the parallel portion 9B, enabling the parallel portion 9B tocome off the presser plate 13. Accordingly, when the explosive 19A isexploded in a state where the airbag 2 is expanded, the cloth-like piece9 is pulled toward the outer peripheral side of the airbag 2 due to atensile force acting on the attachment side base cloth 3 and theparallel portion 9B comes off the presser plate 13. Igniting timing ofthe ignitor 20 is determined by detecting whether the occupant sits downon the seat in the vicinity of the airbag device or not. There areconcrete examples, as a detection method, such as a method of detectingthe occupant by means of a CCD camera, and an infrared sensor, a methodof detecting a magnitude or a distribution of a load of the occupantapplied to the seat by a load sensor, and the like.

As shown in FIG. 2, as for a length from the sewn portion 10 to theright periphery 13A of the presser plate 13 is set such that L1 isshorter than L2 where L2 indicates a length at the attachment side basecloth 3 side while L1 indicates a length at the cloth-like piece 9 side.Accordingly, when the airbag 2 is expanded due to a pressure of gasflown in, the cloth-like piece 9 having the short length is stretchedlinearly while the attachment side base cloth 3 side having the longlength is expanded substantially in circular-arc to move away from thecloth-like piece 9 outward, so that the vent hole 8 keeps open.Particularly an arc-like pocket 22 defined between the sewn portion 10and the vent hole 8 functions as a gas reservoir for interrupting a flowof gas directing from the gas inflow port 5 toward the opposed side basecloth 4 to function to guide the interrupted gas into the vent hole 8,thereby discharging the gas efficiently outward from the vent hole 8 sothat the airbag 2 is expanded while a speed of the gas directing towardthe occupant is reduced. By changing the length L2 at the attachmentside base cloth 3 side, the length L1 at the cloth-like piece 9 side, adistance d from the outer end of the vent hole 8 to the sewn portion 10,and a width W of the parallel portion 9B appropriately, discharge amountof the gas from the vent hole 8 can be changed and an expanding speedcan be suitably adjusted depending on the size of the airbag 2 and thelike.

Now operation of the airbag device according to the first embodiment ofthe invention is described as follows. That is, in the case where thevehicle comes into collision while traveling, when an accelerationsensor detects that an acceleration of collision exceeds a set value,gas is discharged from the inflator 6 and the gas flows in the airbag 2through the gas inflow port 5, thereby developing the folded airbag 2 toexpand. When the airbag 2 is expanded as shown in FIG. 2, the cloth-likepiece 9 stretches linearly due to the tensile force of the airbag 2,while the attachment side base cloth 3 at the vent hole 8 side movesaway from the cloth-like piece 9 outwardly to expand in generallycircular-arc, thereby keeping the vent hole 8 in an open state. At thispoint in time, since the arc-like pocket 22 formed between the sewnportion 10 and the vent hole 8 functions as a gas reservoir forinterrupting the flow of the gas directing toward the opposed side basecloth 4 side so as to guide the interrupted gas into the vent hole 8,the gas flown in the airbag 2 is efficiently discharged outward throughthe vent hole 8, the airbag 2 is expanded while an impactive expansiondirecting toward the occupant side is eased.

At the time when the airbag 2 is sufficiently developed up and down andleft and right relative to the occupant to become a sufficient size toprotect the occupant, the ignitor 20 is ignited to ignite the explosive19A in the explosive chamber 19 so that the necking portions 17A, 17A ofthe retaining plate 17 are instantaneously bent due to a gas pressurecaused by the explosion of the explosive 19A. The retaining plate 17 isbent up to the position as shown by two dotted chain lines in FIG. 6, sothat the retaining projections 18A, 18B come off the retaining holes16A, 16B of the cloth-like piece 9. Since a tensile force is applied tothe cloth-like piece 9 by an expansion force of the attachment side basecloth 3 caused by gas pressure, the parallel portion 9B comes off thepresser plate 13 so that the semi-circular portion 9A is brought intointimate contact with the attachment side base cloth 3 due to a gaspressure as shown in FIG. 3, thereby closing the vent hole 8 by thesemicircular portion 9A to stop the discharge of the gas through thevent hole 8. At this stage, the opposed side base cloth 4 of the airbag2 contacts the occupant so that the opposed side base cloth 4 isslightly expanded by the flowing gas, thereby receiving the occupantsoftly.

An airbag device according to the second embodiment of the invention isnext described hereinafter with reference to the accompanying drawings.The second embodiment is structured such that the closing of a vent hole8 and the switching of the developing height of an airbag are carriedout by a common retaining device. Parts which are the same as those inthe first embodiment are denoted by and described with the samereference numerals. FIG. 7 is a plan view showing a state where anairbag device 1 is expanded, and an inflator 6 is removed. FIG. 8 is asectional view taken along line D-D in FIG. 7 showing a state where theinflator 6 is fitted. As shown in FIG. 7-FIG. 8, the airbag device 1 isformed of the airbag 2 comprised of an attachment side base cloth 3having a circular shape and an opposed side base cloth 4 having also thecircular shape and peripheries of the attachment side base cloth 3 andopposed side base cloth 4 are sewn together and reversed to form theairbag 2 having a bag-like shape. The attachment side base cloth 3 islocated at a side to be fitted to a vehicle together with the inflator 6while the opposed side base cloth 4 is located at a side to face theoccupant and receives the occupant when the airbag 2 is expanded. Theinflator 6 is fitted to a circular gas inflow port 5 formed on thecenter of the attachment side base cloth 3, and gas generated in theinflator 6 flows in the airbag 2 through the gas inflow port 5, toexpand the airbag 2 while developing the airbag 2 in a folded state.There are defined four bolt insertion holes 11A, 11B, 11C and 11D in theattachment side base cloth 3 each spaced at 90 degrees at the peripheralportion of the inflow port 5 of the attachment side base cloth 3, andthe airbag 2 is fitted to the vehicle using these bolt insertion holes11A-11D.

FIG. 10-FIG. 11 show a detailed structure of a metal fitting portion bymeans of which the airbag 2 is fitted to the vehicle, wherein FIG. 10 isan enlarged sectional view taken along line E-E in FIG. 7, FIG. 11 is aview as viewed from an arrow Y in FIG. 10, and FIG. 12 is a sectionalview taken along line F-F in FIG. 11. As shown in FIG. 10 to FIG. 12,the attachment side base cloth 3 is clamped between a substantiallydisc-like presser plate 13 and a metal fitting 12, and it is fixed tothe metal fitting 12 together with a flange 6A of the inflator 6 bymeans of four bolts 14A-14D inserted into the bolt insertion holes11A-11D and nuts 15 screwed into the bolts 14A-14D respectively. In themanner described above, the folded airbag 2 and the metal fitting 12 towhich the inflator 6 is fitted are fixed to a central portion of asteering wheel of the vehicle (not shown).

As shown in FIG. 8, FIG. 10 and FIG. 11, a first tether belt 28 isstretched between an inside end face 6A of the inflator 6 and a centralportion 4A of the opposed side base cloth 4. That is, an upper end ofthe first tether belt 28 is put in the inside end face 6A of theinflator 6 by a presser plate 26, and the presser plate 26 is fixed tothe inside end face 6A by two bolts 25, 25, thereby fixing the firsttether belt 28 to the inside end face 6A. The lower end of the firsttether belt 28 is sewn and fixed to the central portion 4A of theopposed side base cloth 4. Further, a lower end of a second tether belt27 is sewn and fixed to the opposed side base cloth 4 at a substantiallyintermediate position 28A of the first tether belt 28 in thelongitudinal direction thereof. Further, an upper end 27A of the secondtether belt 27 is detachably fitted to the presser plate 13 togetherwith the cloth-like piece 9, described later. In a state where the upperend 27A of the second tether belt 27 is fitted to the presser plate 13,the opposed side base cloth 4 is restricted in its developing height toH1 by the second tether belt 27, and at this point in time, the firsttether belt 28 is rendered in a slackened state at the side over theintermediate position 28A. That is, as shown in FIG. 9, when the upperend 27A of the second tether belt 27 comes off the presser plate 13, theslackness of the first tether belt 28 at the side over the intermediateposition 28A is removed owing to a gas pressure operating on the opposedside base cloth 4, so that the airbag 2 is expanded up to the developingheight H2 which is determined by the full length of the first tetherbelt 28. According to the second embodiment, although the first tetherbelt 28 go slacks at the side over the intermediate position 28A whenthe developing height is restricted to H1 by the second tether belt 27,the first tether belt 28 may not go slacks at the side over theintermediate position 28A. That is, in a state where the opposed sidebase cloth 4 is restricted in developing height to H1 by the secondtether belt 27, the first tether belt 28 is bent in an L-shape at theintermediate position 28A and stretches linearly from the intermediateposition 28A to the upper end of the first tether belt 28. When theupper end 27A of the second tether belt 27 comes off the presser plate13, the first tether belt 28 stretches linearly from the upper end tothe lower end thereof, rendering the developing height to H2.

In the second embodiment shown in FIG. 8 and FIG. 9, although the lowerend of the second tether belt 27 is sewn to the first tether belt 28 atsubstantially the intermediate position 28A of the first tether belt 28in the longitudinal direction, it may be sewn to the opposed side basecloth 4 (at the position in the vicinity of the central portion 4A towhich the lower end of the first tether belt 28 is sewn). In this case,it is sufficient to set the length of the second tether belt 27 from theupper end to the lower end to be smaller than the length of the firsttether belt 28 from the upper end to the lower end thereof. In themanner described above, in a state where the upper end 27A of the secondtether belt 27 is fitted to the presser plate 13, the opposed side basecloth 4 is restricted to be low in the developing height by the lengthof the second tether belt 27 from the upper end to the lower end, and atthis point in time, the first tether belt 28 is caused to go slack atthe entire length. Then, when the upper end 27A of the second tetherbelt 27 comes off the presser plate 13, the first tether belt 28 has noslackness due to gas pressure applied to the opposed side base cloth 4,so that the airbag 2 is expanded up to the developing height which isdetermined by the entire length of the first tether belt 28.

As shown in FIG. 7, three vent holes 7A, 7B and 8 are defined in theattachment side base cloth 3 for discharging gas flowing in the airbag 2outward. Two vent holes 7A, 7B are formed at positions which are equallyspaced from a center 5A of the gas inflow port 5 in a radial direction,while the gas vent hole 8 is formed at a position spaced outwardly fromthe center 5A of the gas inflow port 5 in a radial direction whileopposing the vent holes 7A, 7B, wherein a distance from the vent hole 8to the center 5A is longer than that from the vent holes 7A, 7B to thecenter 5A. As shown by dotted lines in FIG. 7, a cloth-like piece 9 forclosing the vent hole 8 is fitted to the inside of the attachment sidebase cloth 3. The cloth-like piece 9 has a length extending outwardlyfrom the peripheral portion of the gas inflow port 5 and exceeding theouter end of the vent hole 8, and it is comprised of a parallel portion9B extending outwardly in the radial direction from the peripheralportion of the gas inflow port 5 and a semicircular portion 9A having acurvature radius which is larger than that of the vent hole 8, and madeof a cloth which is the same material as the airbag 2. The cloth-likepiece 9 may be made of a cloth which is different from the material ofthe airbag 2. Further, the cloth-like piece 9 is not limited to a clothand may be formed of a sheet-like material such as plastics and the likeif the material has a flexibility capable of closing the vent hole 8.The cloth-like piece 9 is sewn and fixed to the attachment side basecloth 3 at a coordinate axis position X2 which is spaced by a distance din an outward radial direction from a coordinate axis position X1extending in the direction of X from the center 5A of the gas inflowport 5 to the edge of the vent hole 8 in the radial direction. A sewnportion 10 of the cloth-like piece 9 has a circular-arc shape and spacedfrom the edge of the vent hole 8. A width W of the parallel portion 9Bof the cloth-like piece 9 is set to be larger than a diameter of thevent hole 8 and has a width which is sufficient to completely close thevent hole 8. When the width W of the parallel portion 9B of thecloth-like piece 9 is made smaller than the diameter of the vent hole 8,the vent hole 8 is not completely closed but it is possible to controlthe vent hole 8 so as to discharge gas slightly.

The parallel portion 9B and the upper end 27A of the second tether belt27 are detachably fitted to a presser plate 13 at the peripheral portionside of the gas inflow port 5. That is, as shown in FIG. 7, there aredefined two retaining holes 16A, 16B in the parallel portion 9B, theupper end 27A of the second tether belt 27, and the attachment side basecloth 3 between the bolt insertion holes 11D, 11C along the samecircumference of the bolt insertion holes 11D, 11C. An ignitor insertionhole 23 through which an ignitor 20 is inserted, is defined in theattachment side base cloth 3 between two retaining holes 16A, 16B whileU-shaped notches 24 are formed on the parallel portion 9B and the upperend 27A of the second tether belt 27, respectively, so as to surroundthe ignitor insertion hole 23. As shown in FIG. 10 and FIG. 11, theparallel portion 9B and the upper end 27A of the second tether belt 27are inserted in a gap defined between the presser plate 13 and theattachment side base cloth 3 while the two retaining holes 16A, 16B arepositioned so as to align with two holes 21A, 21B defined in the presserplate 13. Then, the retaining plate 17 is fixed to the presser plate 13by way of bolts 14C, 14D, while retaining projections 18A, 18B of theretaining plate 17 are inserted into the retaining holes 16A, 16B of theparallel portion 9B and the upper end 27A of the second tether belt 27through two holes 21A, 21B, thereby restraining the parallel portion 9Band the upper end 27A of the second tether belt 27 from not being comeoff the presser plate 13.

An explosive chamber 19 protruding cylindrically toward the inside ofthe airbag 2 is formed on the retaining plate 17 at the intermediateportion between the retaining projections 18A, 18B, while the explosive19A is sealed in the explosive chamber 19. The ignitor 20 for ignitingthe explosive 19A is fitted to the flange 6A of the inflator 6, and thetip end of the ignitor 20 extends to a portion in the vicinity of theexplosive 19A. Since necking portions 17A, 17A are provided on theretaining plate 17, when the explosive 19A in the explosive chamber 19is exploded, the retaining plate 17 is bent along the necking portions17A, 17A due to gas pressure caused by explosion, as shown by two dottedchain lines in FIG. 12, to be subjected to plastic deformation, theretaining projections 18A, 18B come off the retaining holes 16A, 16B ofthe parallel portion 9B and the upper end 27A of the second tether belt27, enabling the parallel portion 9B and the upper end 27A of the secondtether belt 27 to come off the presser plate 13. Accordingly, when theexplosive 19A is exploded in a state where the airbag 2 is expanded, thecloth-like piece 9 is pulled out toward the outer peripheral side of theairbag 2 due to a tensile force operating on the attachment side basecloth 3, and the parallel portion 9B comes off the presser plate 13. Atthe same time, the upper end 27A of the second tether belt 27 is pulledout toward the opposed side base cloth 4 side owing to a tensile forceoperating on the first tether belt 28, to thereby come off the presserplate 13. Igniting timing of the ignitor 20 is determined by detectingas to whether the occupant sits down on the seat in the vicinity of theairbag device or not. There are concrete examples, as a detectionmethod, such as a method of detecting the occupant by means of a CCDcamera, and an infrared sensor, a method of detecting a magnitude or adistribution of a load of the occupant applied to the seat by a loadsensor, and the like.

As shown in FIG. 8, as for a length from the sewn portion 10 to theright periphery 13A of the presser plate 13 is set such that L1 isshorter than L2 where L2 indicates a length at the attachment side basecloth 3 side while L1 indicates a length at the cloth-like piece 9 side.Accordingly, when the airbag 2 is expanded due to a pressure of gasintroduced in the airbag 2, the cloth-like piece 9 having the shortlength is stretched linearly while the attachment side base cloth 3 sidehaving the long length is expanded substantially in circular-arc to moveaway from the cloth-like piece 9 outward, so that the vent hole 8 keepsopen. Particularly an arc-like pocket 22 defined between the sewnportion 10 and the vent hole 8 functions as a gas reservoir forinterrupting a flow of gas directing from the gas inflow port 5 towardthe opposed side base cloth 4 to function to guide the interrupted gasinto the vent hole 8, thereby discharging the gas efficiently outwardfrom the vent hole 8 so that the airbag 2 is slowly expanded while aspeed of the airbag 2 gas directing toward the occupant is reduced. Ifthe length L2 at the attachment side base cloth 3 side, the length L1 atthe cloth-like piece 9 side, a distance d from the outer end of the venthole 8 to the sewn portion 10, and a width W of the parallel portion 9Bare changed appropriately, respectively, discharge amount of the gasfrom the vent hole 8 is changed so that an expanding speed of the airbag2 can be suitably adjusted depending on the size of the airbag 2 and thelike.

An airbag device according to the third embodiment of the invention isnext described hereinafter with reference to the accompanying drawings.The third embodiment is structured such that the shape of the cloth-likepiece of the first embodiment is changed to a simple shape and partswhich are the same as those in the first embodiment are denoted by anddescribed with the same reference numerals.

FIG. 13 is a perspective view of a cloth-like piece of an airbag deviceaccording to the third embodiment of the invention. As shown in FIG. 13,a rectangular cloth-like piece 30 which is long in right and leftdirection for closing a vent hole 8 is fitted to an inside of anattachment side base cloth 3. The cloth-like piece 30 is sewn to andfixed to the attachment side base cloth 3 at sewing portion 32A, 32B atboth ends spaced from an edge of the vent hole 8. A width W of thecloth-like piece 30 is set to be larger than a diameter of the vent hole8 and is sufficient to completely close the vent hole 8. A lower end ofan extension cloth 31 is fixed to the cloth-like piece 30 atsubstantially central portion thereof in the right and left longitudinaldirection, and two retaining holes 16A, 16B are defined in the extensioncloth 31 at the upper end. A material of the extension cloth 31 may bethe same as the airbag 2 or may be different from the airbag 2. Further,the extension cloth 31 is not limited to be made of a cloth but may bemade of a material such as plastics and the like if it has flexibility.The extension cloth 31 may be integrally formed with the cloth-likepiece 30. The retaining holes 16A, 16B of the extension cloth 31 at theupper end are retained by a retaining device 17 as explained in thefirst embodiment, and the retention is released at given timing, so thatthe cloth-like piece 30 is pressed toward the attachment side base cloth3 by a gas pressure to close the vent hole 8. That is, when retainingprojections 18A, 18B of the retaining plate 17 (not shown), as explainedin the first embodiment, is inserted into the retaining holes 16A, 16Bdefined in the upper end of the extension cloth 31, the extension cloth31 is restrained not to be come off the presser plate 13.

When the airbag 2 is expanded owing to gas let out from an inflator 6 atthe time of collision of the vehicle, the extension cloth 31 isstretched linearly by a tensile force of the airbag 2, so that thecloth-like piece 30 is pulled toward the inside of the airbag 2. As aresult, the cloth-like piece 30 is moved away from the attachment sidebase cloth 3, and expanded in a substantially circular arc to form a gap33 having a substantially circular arc between the cloth-like piece 30and the attachment side base cloth 3, thereby keeping a state where thevent hole 8 is opened (FIG. 14). Accordingly, gas flown in the airbag 2is discharged efficiently outward from the vent hole 8, so that theairbag 2 is expanded while an impactive expansion directing toward theoccupant is eased. When the airbag 2 becomes a sufficient size toprotect the occupant, the explosive 19A is ignited to generate a gaspressure, which causes the retaining plate 17 to be instantaneously bentat the necking portions 17A. The retaining projections 18A, 18B come offthe retaining holes 16A, 16B of the extension cloth 31. Since a tensileforce based on the expansion force of the attachment side base cloth 3caused by the gas pressure is added to the extension cloth 31, theextension cloth 31 comes off the presser plate 13, so that thecloth-like piece 30 is brought into intimate contact with the attachmentside base cloth 3 owing to the gas pressure as shown in FIG. 15, therebyclosing the vent hole 8 to stop the discharge of gas from the vent hole8. At this stage, the opposed side base cloth 4 of the airbag 2 contactsthe occupant, so that the opposed side base cloth 4 somewhat expandsowing to inflowing gas to receive the occupant softly.

1. An airbag device having an inflator for generating gas and an airbagexpandable by the gas, said airbag device comprising: a gas inflow portprovided in the airbag through which the gas flows in, a vent holeprovided in the airbag for discharging the gas flown in the airbag, acloth-like piece connected to a vicinity of the vent hole at one endthereof, and to a vicinity of the gas inflow port at the other endthereof releasably, wherein said cloth-like piece does not close thevent hole in a state where the other end is retained, and closes thevent hole due to an internal pressure of the airbag in a state where theother end is released, a retaining device for retaining the other end ofthe cloth-like piece, and releasing means for releasing retention of theretaining device, wherein the retaining device has a retaining plate,and the releasing means implements releasing by forcibly deforming theretaining plate.
 2. The airbag device according to claim 1, wherein thereleasing means implements releasing by forcibly deforming the retainingplate by a pressure generated by an explosive.